1. Field of the Invention:
This invention relates to alarm systems and, more specifically, to a water entry alarm system which will generate an audible alarm signal when a protected non-swimmer has entered a body of water and which prevents noise around the body of water from falsely triggering the audible alarm.
2. Description of the Prior Art:
Throughout the world, specifically in the United States, numerous deaths occur due to small children, or other non-swimmers, accidentally falling into swimming pools. The problem has become so severe in certain areas of the United States that local ordinances require that protective fencing be placed around all newly built swimming pools. Even with protective fencing, accidental drownings of small children still occur due to holes in the fencing or, more commonly, unlocked fencing gates.
Numerous devices have been designed and built which will generate an audible alarm signal when a person has accidentally fallen into a swimming pool. U.S. Pat. No. 3,810,146, issued to Lieb, discloses an alarm system for warning people when a non-swimmer has fallen into a swimming pool. The alarm system uses a receiver which senses signals generated by a transmitter which is worn by the non-swimmer. When the receiver senses the signal, it will sound the audible alarm. While the alarm system does work, it is susceptible to signals which may falsely sound the alarm system. The receiver has no way to distinguish if the signal received was generated by the transmitter, or if the signal was generated by outside noise around the swimming pool. Furthermore, the sensing device requires a 110 VAC power source which raises the possibility of electrical shock in and around the swimming pool.
U.S. Pat. No. 5,049,859, issued to Arnell, discloses another water entry alarm system. The alarm system of Arnell is similar in design to Lieb. The alarm system uses a receiver which senses signals generated by a transmitter which is worn by the non-swimmer. When the receiver senses the signal, it will sound an audible alarm. The Arnell transmitter generates a low frequency signal generally in the range of 1 kHz to 10 kHz. The problem with this is that low frequency signals in the 1 kHz to 10 kHz range are present in large quantities in the pool environment (i.e., pool cleaning equipment, pool pumps, external noise, etc). These conditions make it extremely difficult to reliably detect alarm conditions. Thus, like Lieb, the Arnell system is susceptible to signals which may falsely sound the alarm system. The Arnell receiver has no way to distinguish if the signal received was generated by the transmitter or if the signal was generated by outside noise around the swimming pool. Another problem with the Arnell receiver is that it uses a hydrophone. Hydrophones are extremely expensive underwater receivers which makes the system cost prohibitive to the average consumer. Furthermore, like the Lieb system, the Arnell receiver requires a 110 VAC power source which raises the possibility of electrical shock in and around the swimming pool.
Another pool alarm system is disclosed in U.S. Pat. No. 5,144,285, issued to Gore. The Gore system is similar to the two previous alarm systems in that it uses a transmitter-receiver to generate an audible alarm. The transmitter in Gore generates a swept frequency signal. If the receiver senses a signal in the swept frequency range, an audible alarm will sound. Like the two previous systems, the Gore system is susceptible to false alarms. The larger the swept frequency range that the receiver will sense for, the greater the possibility of outside noise falsely generating the audible alarm. Furthermore, like the Arnell system, the Gore system has two other problems. First, the receiver in Gore uses a hydrophone. As stated above, hydrophones are expensive underwater receivers which makes the alarm system cost prohibitive. Furthermore, the Gore receiver requires a 110 VAC power supply. As stated above, the use of an AC power source increases the possibility of electrical shock in and around the swimming pool.
Therefore, a need existed to provide an improved water entry alarm system. The improved water entry alarm system must not be susceptible to outside noise which may falsely trigger the alarm system. The improved alarm system must have a receiver which is able to distinguish whether the signal received was that of the transmitter or if the signal was generated by outside noise around the body of water. The improved water entry alarm system must also be inexpensive to build and maintain thus making the alarm system economically viable to the average consumer.